Thermoelectricity



March ,1963 c. M. HENDERSON ETA]. 3,081,361

THERMOELECTRICITY 5 Sheets-Sheet 1 Filed June 9, 1961 THERMOELECTRIC POWER (SW8 TEMPERATURE TEMPERATURE C. f-

FIGURE WEIGHT PERCENT OF GERMANIUM i I III $506.] 4 l ll 8 6 5 Town- 9 N moho m FEM-z INVENTORS COURTLAND M. HENDERSON DARREL M. HARRIS BY FIGURE 2.

ATTORNEY March 12, 1963 c. M. HENDERSON ETAL 3,081,361

THERMOELECTRICITY Filed June 9, 1961 5 Sheets-Sheet 2 FIGURE 3.

FLAME OR OTHER 2:! HEAT SOURCE 232 262 4/ k\\ 558 559 N P N P rL-jij w F [G u R E 4 INVENTORS COURTLAND M. HENDERSON BY DARREL M. HIQRRIS ATTORNEY March 1963 c. M. HENDERSON ETAI. 3,081,361

THERMOELECTRICITY Filed June 9, 1961 5 Sheets-Sheet 3 ?V A M 65 67 6 I 6 mm FLOW OF HOT EXHAUST OR REACTOR MEDIA 7| Fl R 7 x q Q vs i% 77 Q /A\ 72 73 EIQURE s COOLED PRODUCT f A I91- B. r 58 w INVENTORS COURTLAND M. HENDERSON HOT PRODUCT BYDARREL M. HARRIS ATTORNEY March 12, 1963 c. M. HENDERSON ETAL 3,

THERMOELEC'IRICITY Filed June 9, 1961 5 Sheets-Sheet 4 Fl R l2.

INVENTORS COURTLAND M. HENDERSON DARREL M. HARRIS BY Mim- ATTORNEY March 12, 1963 M. HENDERSON ETAI. 3,081,361

THERMOELECTRIGITY Filed June 9, 1961 5 Sheets-Sheet 5' E B C 305 +304 N P N sow-Milli +309 FIGURE [3.

LIQUID PHOSPHOROUS AIR+1 INVENTO COURTLANO M. HENDE N DARREL M. HARRIS ATTORN EY United States Patent 3,081,361 THERMOELECTRICITY Courtland M. Henderson, Xenia, and Darrel M. Harris,

Dayton, Ohio, assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware Filed June 9, 1961, Ser. No. 116,150 13 Claims. (Cl. 136-4) The present invention relates to improved thermoelectric processes and composition which are of utility for the direct conversion of heat to electricity. The invention also relates to methods of manufacturing the said compositions. The invention includes processes for generating electric power, as well as heating and cooling by the use of the said materials. The present invention also relates to the use of modified boron materials in dielectric (such as a capacitor), thermistor, transistor, rectifier and other semiconductor applications and devices which are of utility in the field of electronics.

While earlier investigators of boron materials have shown a knowledge of the use of such materials as thermocouples, these early compositions like those of conventional thermocouples such as chromelalumel or iron-constantan exhibited poor power generative characteristics. This is indicated by the uniform lack of the use of prior art thermocouples as energy converters of power generators and Peltier cooling units. It is an objective of the present invention to provide unusually effective power generation and Peltier cooling units by means of special composition of germanium as a major modifier or dopant for boron.

The thermoelectric materials contemplated in the present invention are composed of boron having intimately dispersed therein specific proportions of germanium and certain other elements. The germanium is present at lower levels of concentration than stoichiometric rations, e.g., germanium hexaboride. The production of the present combinations of boron together with additive proportions of germanium or other elements is accomplished by various means discussed herein, such as hot-pressing a mixture of elemental boron together with the desired proportions of the desired elements, or the use of precursor materials which, upon processing, decompose to yield boron with the desired elements being present to combine with the boron in the specific proportions herein set forth. Thus, a germanium halide compound such as trichlorogermane has been found to be decomposed either alone, or in conjunction with diborane or boron trihalide at temperatures ranging from 400 C. to 3,000" C. to bring about the deposition of boron with germanium in any desired proportion. Similarly, the use of mixed halides of boron with decomposable hydrides or halides of doping elements (e.g., aluminum, titanium, iron, silicon, carbon, etc.) is employed to produce boron-germanium thermoelectric materials of unique compositions for various power generation, heating, cooling and semiconductor applications.

It is also an advantage of the present invention that electrical and thermal leads capable of operating for long periods of time at temperatures ranging from 200 C. to 900 C. in contact with boron have been made possible. The problem of maintaining ohmic type contacts with boron has been a major obstacle to past workers who tried to determine the thermoelectric properties of boron above 600 C. This investigation has shown that leads of various metals (e.g., Zirconium) or other materials (e.g., hafnium boride) can be attached, by the hot-pressing process discussed with other methods herein, to pure and chemically modified boron pressed shapes to yield units capable of operating over temperatures ranging from 200 C. to 900 C., in air and other media. In air, the compositions of the invention have been found to be modified at high temperatures in that a protective film forms on the boron surface which protects it from further oxidation. A thin coating of non-conducting ceramic material such as zirconia, beryllia, porcelain, alumina and other materials applied by conventional means (e.g., ceramic dipping and flame spraying) can also be used to protect both the electrical leads and the boron-germanium elements.

In general, a second component which is in electrical and thermal contact, e.g., at the hot junction with the first member of germanium modified boron is selected from the group consisting of carbon, copper, gold, silver, nickel, cobalt, iron, rhenium, vanadium, tungsten, molybdenum, hafnium, niobium, titanium, tantalum, beryllium and the oxides, borides, carbides, silicides and nitrides of nickel, cobalt, iron, rhenium, vanadium, hafnium, niobium, titanium, tantalum, tungsten, molybdenum and beryllium.

In a preferred embodiment of the invention, the said second element is characterized by an electrical conductivity and a thermal conductivity which are at least equal in magnitude to the respective electrical and thermal conductivities of the aforesaid boron-germanium element. In the employment of the power generating combination of the herein described first and second elements, a cold lead or third component of various means such as wires, rods, bars and other conductors, electrically and thermally connect the respective elements to an external circuit.

It is an advantage of the present invention that boronbased materials, such as boron-germanium as a binary, boron-lanthanum-germanium and boron-titanium-germanium as typical ternaries, and boron-beryllium-carbongermanium as a typical quaternary are useful as thermoelectric materials, e.g., for obtaining electricity from heat sources below 900 C.

The drawings of this patent application show various specific embodiments and examples of the invention, and data illustrative of the present compositions. FIGURE 1 shows the Seebeck coefiicient of a typical germanium modified boron composition of this invention as compared with other thermoelectric materials for the same temperature range. FIGURE 2 shows the effect of germanium content on the merit factor, Z, of various temperatures. FIGURES 3, 4, 5, 6, 7 and 9 illustrate various thermoelectric generating devices, while FIGURE 8 shows an electrical circuit used with a multiplicity of units. FIG- URE 10 shows the use of boron-germanium materials as a capacitor device for remote control purposes. FIG- URE 11 illustrates the use of boron-germanium materials for rectification purposes. Transistor applications are depicted for boron-germanium materials in FIGURE 13. The use of boron-germanium materials -to recover heat in the form of electric power and for cooling purposes in the processing of phosphorus are shown in FIGURES 8 and 14.

In the embodiment of the invention in which the germanium-boron materials are used as a thermoelectric material, the present combinations of boron-germanium doped with carbon, aluminum, beryllium, magnesium, silicon, tin, phosphorus, titanium, zirconium, hafnium, co balt, manganese and the rare earths of type 4f are advantageously employed. These combinations are characterized by an unusually high stability of the Seebeck coefiicien-t at elevated temperatures as shown, for example, in FIGURE 1 where the relationship between the thermoelectric effect (Seebeck coefiicient, S) and the temperature is shown for a typical germaniumboron material with 15% by weight germanium and compared with lead selenide, element 2, and indium arsenic phosphide, element 3, as representative of the best prior art materials. In this relationship, it has been found that the germanium-boron material typified here is useful as a thermoelectric power generating substance at temperatures above those at which conventional metallic type thermoelectric generating compositions may be employed. For example, indium phosphide has been investigated as a high-temperature, power-generation material, but has been (found to be ineffective at temperatures greater than 800 C. In contrast thereto, the present materials function as effective thermoelectric generator components at temperatures as low as 110 C. and are of particular utility at temperatures from 300 C. to 925 C. The present materials may therefore be used in power generation devices located in the motor exhausts, tail, wing and nose surfaces of missiles and rockets, in atomic energy reactor linings, in exhaust stacks of chemical reactors, in petroleum processing units, etc. Thus, in employing a germanium-boron based thermoelectric combination of the present invention in the wall of an atomic energy reactor or in various types of chemical reactors, it is found that the removal of heat through this material serves to generate electricity which is usable for prime power generation and also for the purpose of cooling the walls of such equipment. It is well known that there are numerous problems in the chemical, nuclear, missile and space craft fields where it is advantageous to cool the walls and exhaust stacks of chemical and nuclear reactors desirably by some means other than conventional liquid or gaseous systems. It is possible by the present invention using germanium-boron compositions to simultaneously accomplish power generation and safe cooling of linings of chemical reactors and exhaust gas stacks, rocket chambers and exhaust nozzles, hot surfaces and bearings of space craft.

The present materials therefore constitute a solid state electronic device for lowering the temperatures of reactor linings, thus reducing the use of liquids and gases which can be dangerously volatile in such applications. The present solid state cooling devices of this invention also permit the location of specially shaped coolant members, particularly in critical, hard-to-cool sites such as in chemical reactors, hot mechanical hearings or hightemperature electronic devices. A further advantage in the use of such solid state cooling devices is that they offer self-regulating, self-powered, smooth-temperature control which minimizes thermal stresses and maintenance of wall linings as Well as a minimum of instrumentation for control purposes. In addition, it is noteworthy that there are no moving parts and little maintenance requirements in the use of these materials.

The individual thermoelectric generating, and also solid-state cooling elements employed in the present invention are founded upon thermoelectric units of the aforesaid germanium-boron material in which germanium is present in the boron. With germanium, the range is generally from 0.05% to 45% by weight germanium in boron to form a thermoelectric unit. More preferably, the range of germanium content in boron is from 0.5% to 40% by weight. Still more preferably, the germanium content is from 1.0% to 35% by weight in boron to form the most effective thermoelectric units. Such units are comprised of the germanium-boron component, with each end thereof joined to highly conducting leads by fusion under pressure or hot-pressing methods. An example of such an electrically and thermally conducting lead material is graphite, a form of carbon. 'I'his thermoelectric unit may be utilized per se, for example, as concentric outer and inner cylinders of carbon in contact with an intermediate concentric layer of the germanium-boron material as shown in FIGURE 5. Another modification is to join plate-like germanium-boron elements to carbon or other conducting contacts in a sandwich-like configuration as shown in FIGURES 3 and 9. Multiple junctions may be made by conventional means using concentric and/or sandwich-type units joined in series electrical connections or parallel electric connections. Various shaped objects, for example, liners for high temperature exhaust stacks of atomic reactors may similarly be provided in this manner. In this relationship, the thermal and chemical stability of the germanium-boron combination is of particular utility. A chemical vessel may also, for example, be provided with sandwich or concentric type thermoelectric units made of germanium-boron thermoelectric generator materials.

Example 1 FIGURE 5 shows a typical cross section view of a portion of a chemical reactor or hot exhaust stack. Elements A and B are identical thermoelectric units separated by an electrically insulating section, element 68. As shown in FIGURE 5, the boron-germanium material 61 is joined to conducting material 62 and 63 which consist, for example, of carbon, nickel or beryllium oxide to form individual thermoelectric units. The inner conducting material 61 is joined to the inner lining 69 of a refractory metallic, cermet, or ceramic conducting type, or element '62 may itself serve as the inner lining. For example, carbon, nickel alloys and beryllium oxide make excellent corrosion resistant linings for chemical reactors. Furthermore, these materials have desirable thermal and electrical conductivities useful in this relationship.

In FIGURE 5, elements 64 and 65 represent the junc :tions of the conducting layers 62 and 63 respectively with the boron-based element 61. Elements 66 and 67 are the electrical leads connecting elements 62 and 63 respectively to external circuits A and B.

It is often desirable to employ several individual units in series or parallel. In such instances, an electrical and thermal insulator 68 is used between the individual sections.

The present thermoelectric units can be used to form the walls of reactors, or units of these materials can be embedded a suitable distance below the surface of the wall. Such units which include boron-based material may be placed in contact with the innermost wall of the vessel by mechanical means or may be deposited in place, for example, by flame-spray coating methods. Thus, there is obtained a combination generator-cooling unit as a part of a. chemical reactor vessel. When the unit of FIGURE 5 using the aforesaid materials is subjected to heat at the inner junction 64 of the boronbased material 61 and its outer junction 65 is cooled, electrical energy is generated by the unit which can be utilized as an electrical power source section A. This thermoelectric power generation absorbs heat through the hot inner surface of the lining 69 of the reactor wall, thus cooling it. Automatic temperature control results when the cooling section B is placed upstream (or near the hottest section of the reactor) of the power genera-tor unit A. Various combinations of thermoelectric units, through proper electrical switching, may be used entirely for power generation or cooling or any power-cooling combinations.

If desired, greater cooling capacity can be produced by utilizing power from an external source as shown, for example, in FIGURE 8 where power source 99 may be polarized to oppose current I or to flow with it forming a combined current 1 4-1 as desired. It is understood that by reversing current flow in a thermoelectric cooling unit through application of an external power source that heating of the reactor walls prior to start up or for preheating reactants may also be achieved.

FIGURES 3, 4, 5, 6, 7 and 9 of the present patent application illustrate more specific embodiments and examples of the invention.

Example 2 FIGURE 9 shows a thermoelectric power production unit in which the boron-germanium material (element 21) with about 14 weight percent of germanium, which may optionally contain additional doping elements dispersed within the boron as the matrix, is joined to conducting electrical leads 20 and 23. Such leads, or junc tions, may be conventional conductive metals and compounds such as iron, nickel alloys or beryllium oxide. The junction is made by fusing the metal or compound into the germanium-boron material, or by spraying (e.g., flame or plasma) or plating (under vacuum or atmospheric conditions, preferably with an inert atmosphere) on the faces 24 and 25 of the thermoelectric material 21 followed by fusing or pressure contacting with materials of 29 and 23 with faces 24 and 25 respectively. External circuit contacts are then made by conventional means such as soldering, welding or pressing of external circuit conductors to leads 26 and 27. In order to obtain an electrical current from the thermoelectric unit 21, an end 20 of this germanium-boron material is heated by heat source 9, while the other end 23 is cooled. This produces a temperature differential across faces 24 and 25 which re sults in conductor 20 becoming positively (boron-germanium used alone or with certain dopants) or negatively charged according to the doping materials used in the germanium-boron. The collection of positive and negative charges at faces 24 and 25 generates electrical power, i.e., current and voltage at a substantial wattage, which, when connected through leads 26 and 27 to external loads 28 and 29 through switches 10, can perform useful work. With unit 21 of dimensions of 1 square centimeter cross section operating between 900 C. and 250 C. and with a Z merit factor of 0.3l l0 C., a power output of 5.7 watts is obtained.

Highly useful thermoelectric power generation devices are also obtained when doped boron-germanium compositions are employed. For example, when element 21 consists of 85.90 weight percent boron, 0.03 weight percent titanium and 14.07 germanium, and a temperature differential of 600 C. is maintained across faces 24 and 25, a power flux of 4.5 watts/cm. is obtained. Higher power output is obtained when specific, select materials are used for elements 20 and 23 in a manner to augment the power generation characteristics. That is, when the heat source is located at or near element 24, it is important that element 20 be an n-type conductor, such as constantan, while element 23 should be a p-type, such as carbon. In this manner, the smaller but valuable thermoelectric effect of the leads is added to the power output from the boron-based materials. For example, when elements 20 and 23 are selected with the polarity described above, the power output for the device is thermally more efiicient than when the leads of reversed polarity to that prescribed are used.

A further important aspect of the generator device shown in FIGURE 9 is that elements 24 and 25 may be formed by partially diffusing elements 20, 21 and 23 to form junctions or interfaces which exhibit a gradual or gradated change in thermoelectric properties for a traverse from right to left from element 23 (i.e., carbon) to a combination of carbon with boron-titanium-germanium at element 25 and then to boron-titanium-germanium in a single body, element 21. Similarly, the thermoelectric properties and composition changes for a further continuation of a right to left traverse from element 21 (bouon-titanium-germanium) to a combination of boron titaniumgermanium and constantan. The use of gradated junctions such as these, which are readily fabricated by hot pressing, is advantageous in overcoming junction problems of low strength and poor thermal and electrical characteristics.

The availability of nand p-type boron-germanium materials perrnits wide flexibility in the design and use conditions for thermoelectric generators made of these compositions. When using p-type boron-germanium, other component materials may be used as the n-type element, such as doped, silicon carbide.

In addition to the above direct use of the boron-germanium thermoelectric material, another field of application is in combinations of this unique high-temperature product with lower-temperature thermoelectric materials.

Example 3 FIGURE 3 shows a thermoelectric power generator in which high-temperature boron-germanium material 231 (12 weight percent germanium) is connected thermally and electrically in series with lower-temperature thermoelectric materials 241 (for example, indium arsenic phosphide, 242 (lead telluride) and 243 (bismuth selenide). By controlling the thickness of such typical materials 241, 242 and 243 with the germanium-boron product, the thermal gradient across each material can be controlled and optimized. In this process, the peak or optimum efiiciency for each material can be utilized. In FIGURE 3, showing a cross section of the thermoelectric device, heat from combustion 23-2, chemical waste heat, nuclear or other (e.g., solar) sources is directed through hot junction component 247 to heat junction 26 0. Through the use of refractory metals or compounds (e.g., nickel metal and other heat resistant metals and alloys, or beryllium oxide) for element 247, heat sources below 925 C. can be used to heat the junction 260. Due to the low thermal conductivity of the boron-germanium material, the temperature at the junction 280 between materials 231 and 241 can be maintained at a desirable lower (e.g., SOD-600 C. as indicated by the temperature versus Seebeck coefficient relationship in FIGURE 1) temperature Where material 241 (e.g., indium arsenic phosphide) most effectively operates. Similarly, by controlling the thickness of the layer of material 241, the temperature at the barrier 28 1 between materials 241 and 242 can be dropped to a still lower temperature (e.g., about 350 C.) where lead telluride or a similar material operates at peak efficiency. Finally, the cold lead component 233, consisting of a central hollow cylinder of high thermal and electrical conductivity, is partially filled with a condensable liquid 244 (e.g., water, mercury, etc.). This condensable liquid maintains a nearly constant temperature for junction 273 through evaporation of vapor from the liquid 244. The vapor condenses on cooled (by radiation, conduction and/ or convection) top portions of component 233 and at surface 245 and on the side walls, thereby releasing heat to the finned or otherwise cooled portion 233 of the generator unit. Diffusion barniers 280, 28 1 and 232' (which lattermost is the junction between 242 and 243), such as nickel, copper, beryllium oxide or other materials, prevent migration of the boron or its modifying elements from one layer to another.

Example 4 Compositions of boron-germanium with various elements or combinations thereof that are useful for high temperature thermoelectric power generation and cooling purposes are presented below. These same compositions are also useful for other semiconductor applications and devices, such as capacitors, dielectrics, thermistors, transistors and rectifiers. In this table, the small x represents weight percent for concentrations of additive elements for the weight percent of the broad range, and preferred concentration range. For the column headed Compositions, the small y indicates the weight percent of germaniumas defined in the ranges above, e.g., broadly 0.05 to 45% and x represents weight percent of the additional additives. For example, in the first horizontal line of Table I, the material BGe Li has the limiting formulae in which the germanium content ranges from 0.05 to 45 weight percent and the lithium from 1 l0- to 18 weight percent.

TABLE I Cooling Properties Weight Percent Elements Element Per. Compositions Group Broad Range Preferred Range I-A 1X10- to 18---- 1X10 to 15..... BGeyLlx. I-B 1 10- to 20--.. 1X10 to 18- BGe Agx, BGe Am,

BGe Cux. II-A 1 l0- to 0.04... 1 10- to 0.04- BGe Srx, BGe Cax,

BGc Bex, BGc Bax. II-B 1X10- to 25---- 1Xl0- to 20 BGe Znx. III-A 1X10- to 25.... 1 10- to 20-.-.- B%%Alf, BGe Gax,

y Ilx- RE,* Y, So, Ac III-B 1 10- to 25.... 1 10- to 20- BGe RE,,* BGe,,Y,,

BGe Scx, BGe Acx. 0, Sn, Pb, Si IV-A 1 10- to 0.04... 1 10- to 0.04"- BGe O,, BGe SnX,

BGeyPbx, BGe SiX. Ti, Zr, Hf IVB 1X10- to 0.04... 1 10- to 0.04'" B(l33tgTififBGe Zrx,

e x. P, Sb, As, Bi V-A 1 10- to 20.... 1X10- to 18..... BGe P,, BGe Sb BGGyAS BGe Bix. Nb, Ta, V V-B l l0 to 25..-. 1Xl0- to 20..-.- BgedNbrx, BGe lax,

Cy x. S, Se, Te, Po VI-A 1 l0- to 20.--. 1 10- to 18--.-. BGOySx, BGo Se,,

BGe 'lex, BGc Pox. Cr, Mo, W VI-B 1X10 to 25-.-- 1X10 to 20 BGcG OiwBGe lvl'o ey x. Mn, Re VII-B 1 10- to 25. 1 l0- to 20--.-- BGe Mm, BGe Rex. 00, Fe, Ni, Ru, Ir, Pd, Rh VIII 1 10" to 25.... 1 l0- to 20. BGQyCOx, BGe Fe,

BGeyNix, BGO RUx, BGe IrX, BGe Pdx, BGeyRhx- RE includes lanthanide and actinide series.

In this group of additives or dopants which are com bined singly or in combination with boron-germanium, the preferred members as discussed above with respect to amounts, are:

Carbon, aluminum, beryllium, magnesium, silicon, tin, phosphorus, titanium, zirconium, hafnium, cobalt, manganese and the rare earths of type 4f.

However, the invention also contemplates certain other compositions as shown in Table I, with specific regard to proportions, both broadly and narrowly. Thus, a grouping of the elements is that the preferred ranges-of elements are present at from 1X10 to Weight percent for Li;

1 lO to 18 weight percent for Ag, Au, Cu, Pb, P, Sb,

As, Bi, S, Se, Te and Po;

1 10- to 20 weight percent for Sr, Ca, Zn, Al, Ga, In, RE, Y, Sc, Nb, Ta, V, Cr, Mo, W, Mn, Re, C0, Fe, -Ni, Ru, Ir, and Pd;

1 10- to 0.04 wt. percent for C, Si, Ti, Zr, Be, Sn and The broad range of proportions includes the range of additives from 1 10- to 18 weight percent for Li;

1 10- to 20 weight percent for Ag, Au, Cu, Pb, P, Sb,

As, Bi, S, Se, Te and Po;

1 10- to weight percent for Sr, Ca, Zn, Al, Ga, In, RE, Y, Sc, Nb, Ta, V, Cr, Mo, W, Mn, Re, C0, Fe, Ni, Ru, Ir and Pd;

1X10" to 0.04 Wt. percent for C, Si, Ti, Zr, Be, Sn and four different thermoelectric segments, elements 231, 241, 242 and 243 which can also be represented by FIG- URE 3. These segments consist of doped germaniumboron compositions which are joined into a unitary body. For example, in a structure like that shown in FIGURE 3, element 231 is made from 10 weight percent germanium in boron to which has been added 0.02 weight percent carbon; element 241 is composed of 11 weight percent germanium in boron doped with 0.03 weight percent carbon and with 0.04 Weight percent titanium; element 242 consists of '15 weight percent germanium in boron to which has been added 0.03 weight percent silicon and element 243 consists of a high Z factor type lead selenide. When this unit is operated over a temperature range 925 C. at the hot junction (element 260), and C. at the cold junction (element 273), the unit produces 6 watts per square centimeter of cross section perpendicular to the vertical flow of heat from element 247 to element 232 The individual segments or the cascaded units are made by inserting a hot junction component, element 247, con sisting of a typical heat resistant alloy of 76 weight percent iron, 23 weight percent chromium, and 5 weight percent aluminum into a graphite-boron nitride-lined die, then charging enough of the mechanically blended .10 weight percent germanium in boron plus 0.03 weight percent carbon powder mixture on top of element 247. A male die plunger mechanically compacts this powder mixture 241 on top of element 247. Next, a thin layer of powdered silicon carbide is charged on top of element 241 and this powder compacted by a stroke of the male die to form a barrier, element 280. Next, the previously mentioned powdered composition for element 242 is charged on top of the last mentioned element 280 and this material is compressed with a stroke of a male die plunger. A second barrier, element 281, consisting of powdered nickel is then formed on top of element 241 by repeating the process used to form element 230 referred to above. The third thermoelectric segment, element 242, is formed by charging the aforesaid powder compositions for this element on top of the last diffusion barrier and repeating the compaction process. Then the three thermoelectric elements, barriers and hot junction components are formed into a unitized element by placing the assembly, while still in the graphite die, into an induction coil assembly. This aforesaid assembly of ele ments 247, 231, 241, 242, 243, 280, 281 and 282 is then heated to a temperature of about 900 vC. and held under a pressure of 2500 psi. for thirty minutes. Following this, the now compacted assembly of elements 231, 241, and 242 is cooled while still within the graphite die and placed under a hopper which charges powdered lead selenide on top of the aforesaid unitized assembly of thermoelectric segments with barriers. The powdered lead selenide mixture is then compacted at room temperature under a pressure of 4000 p.s.i. for a period of ten minutes after which the now unitized assembly consisting of four segmented thermoelectric elements, three barriers and one hot junction component are removed from the die and coated with a silver cement. Element 233, the cold junction component is then attached to the aforesaid unitized assembly of several thermoelectric segmented layers by means of several spring loaded high temperature alloy toggle bolts which compress element 233 on top of the assembly of elements 247, 231, 241, 242, 243, 280, 281 and 282.

Similar devices consisting of several cascaded thermoelectric units with or without diffusion barriers between the segmented elements are manufactured by compacting the individual thermoelectric segments in separate dies under suitably high temperatures and pressures, such as 200 C. and 1500 psi. for element 231, 1800 C. and 1900 psi. for element 241, 650 C. and 5000 p.s.i. for element 242, and 50 C. and 5500 p.s.i. for element 243. The diffusion barriers, elements 280, 281 and 282 are then formed by consecutively placing a thermoelectric segment, element 231, in a die, charging powdered barrier elements 280, 281, and 282, metal or compounds such as nickel, molybdenum, silicon carbide and tungsten between segments and then hot-compacting several segments and barrier elements with one stroke of a male die plunger. High quality junctions of the individual units of this type power generator are also obtained by other methods, using, for example, gravity loading of all the elements to form the device of FIGURE 3 and by cementing the various elements with silver solder and similar joining materials.

It is also found that two'element units yield excellent power outputs, for example, with one body of boron with 10% germanium and with the second element being another thermoelectric body such as boron silicon (0.03 Si), or indium arsenic phosphide, bismuth telluride and lead telluride. The two bodies are maintained in electrical contact, and with external leads to the load.

Example 5 It has been recognized that most combinations of elements, compounds and alloys which produce high Seebeck coetficients and voltage generating characteristics usually do not exhibit high power generation properties. It is apparent from the following known relationship for the thermal efficiency of thermoelectric devices that in addition to a high Seebeck coelficient, it is necessary to use materials which have low electrical resistivity and high thermal conductivity.

Efficiency of Thermoelectric Device h o av)] av)] i where for a typical power generating device of this invention as shown in FIGURE 9:

T =temperature of the hot junction, element 24 T temperature of the cold junction, element 25 T =average absolute temperature of T and T Z =S K=merit factor S=Seebeck coeflicient of element 21 =electrical resistivity of element 21 K thermal conductivity of element 21 From the above relation, it is also obvious that it is highly desirable to use materials which permit operating over a high temperature differential between the hot junction, element 24 of FIGURE 9, and the cold junction, element 25. Often, it is impractical to use cold junctions at temperatures substantially lower than room temperature or as provided by water cooling. It is highly desirable to use thermoelectric power generating; materials which will operate satisfactorily at the highest possible temperature. The Seebeck coeflicient, resistivity and thermal conductivity for most prior art thermoelectric materials tend to decrease with temperature. Further, as shown in the prior art, there are specific ranges of composition of thermoelectric materials which produce most effective and valuable thermocouples as represented by the specific and narrow ranges of composition used for Chromel-Alumel, copper-constantan, and other common thermocouples.

The present invention shows that specific ranges of germanium-boron and also germanium-boronwith additive elements and compounds yield highly unique generating properties over a wide range of temperatures, particularly at very high temperatures. For example, in FIGURE 2 there is presented the Z, or merit factor, for boron-germanium materials of this invention plotted versus germanium content over a wide range of temperatures, 200 C. to 925 C. Since, as shown in Equation I, the efiiciency of power generation for a device is closely related to the merit factor (S /pK), this plot of Z versus germanium content of boron-germanium also represents the relative power generation capabilities of boron materials. Thus, FIG- URE 2 shows that uniquely high merit factors, and therefore uniquely high power generation, is obtained from a device using boron-germanium with a preferred range of 0.05 weight percent germanium to 45 weight percent germanium, a more preferred range of 0.5 weight percent and 40 weight percent germanium and a still more preferred range of 1.0 weight percent to 35 weight percent germanium.

It has been found that high values occur for the material merit factors and power generation capabilities of devices based on ternary and quaternary boron-germanium based materials in the range of 0.05 weight percent to 45 weight percent germanium in boron material doped with one or more elements at additive levels shown in Table I of Example 4. For example, in a typical device as shown in FIGURE 9, with thermoelectric element consisting of a ternary of 10 weight percent germanium, 88 weight percent boron and 2 weight percent cerium produces 1 watt per square centimeter cross section area of element 21 when operating with a temperature differential of 300 C. between junction elements 24 and 25. A further example of the high power generating capabilities of the materials and devices of this invention is seen in the operation of a device of the configuration shown in FIGURE 9 in which element 21 consists of a quaternary of 12 weight percent germanium, 87.95 weight percent boron, 0.02 weight percent carbon, and 0.03 weight percent titanium. When this unit is operated with a temperature differential of 600 C. between junction elements 24 and 25, the device produces 2 watts per square centimeter of cross section of element 21.

Example 6 A remote control device using the present boron-germanium material with 9 weight percent germanium is shown in FIGURE 10. One of the advantages of using the material of this invention is that no mechanical or moving parts are required to change the impedance of the electrical circuit in the control device. For example, when using a 12.5 weight percent germanium in boron material, element 71 of FIGURE 6 or element 81 of FIGURE 7 to produce the capacitor, element 130 of FIGURE 10, it is found that the capacitance of such a unit can be varied by a factor of 75 simply by varying the frequency of the voltage source from cycle-s per second to 100,000 cycles per second. Element 121 in FIGURE 10 represents a radio signal sending device with aerial 125 transmitting radio energy 127 to receiving device 120 which consists of a radio receiving set 120 including a receiving aerial 126 connected to a conventional receiving circuit in which the boron-germanium capacitor element 130 of the present invention, also 71 in FIGURE 6, is connected by leads 131 to cause the transmitted radio energy to build up or decrease the polarized voltage applied across the boron-germanium capacitor 130. The variation of the frequency of the voltage applied across the capacitor 130 causes the dielectric constant of this material to change, thus varying the capacitance of the boron-germanium material 130, and thereby the impedance of the circuits in unit 123 and 122. Unit 122 is typically a motor or electrically actuated lever switch and 123 is a radio circuit which it is desired to tune by remote control or which may be an electrical device for controlling unit 122. More specifically, motor circuit 122 is made to move a switch or lever arm 104 between contacts 128 and 129. Tuneable circuit 123 is similarly controlled by boron-germanium capacitor unit 130, the resistance of which is varied in response to the signal transmitted from sender unit 121.

In addition to the specific embodiment discussed in this example, other capacitor uses of the boron-germanium material include capacitor modified circuits, e.g., containing chokes and condensers. Similarly, other compositions selected from doped boron-germanium listed in Table I are also used for such applications.

FIGURE 11 shows still another configuration useful for a capacitor that can be varied by imposing a variable frequency power source thereon through leads 143 and 144. Element 140 represents the modified boron material sandwiched between junction materials 141 and 142. A use for the device of FIGURE 11 is in FIGURE where it is substituted for elements 130 and 131.

Example 7 In FIGURE 12, device 158 is a point contact rectifier device of the invention. Body 151 in the shape of a disc is suitably a boron-germanium material, such as boron containing 6.5 weight percent germanium and about 0.01 weight percent carbon. For optimum rectifying properties, disc 151 should not be more than about 50 mils thick and preferably not more than about 10 mils thick. The bottom side of disc 151 has been coated with copper, nickel or other metals stipulated herein as electrical junction materials to make ohmic contact therewith and provide a conducting surface for soldering or welding to the disc electrode 152 which is suitably a copper electrode. The upper surface of body 151 is not coated and point contact electrode 153 is suitably a phosphor-bronze or a tungsten whisker, which as pressed against the upper surface of disc 151 to make electrical contact therewith. Suitably a pressure of about 50 grams of force is used pressing the point contact electrode 153 against the top of disc 151; however, this force might vary from about 10 to about 100 grams more or less, for optimum performance. Suitably, the upper end of whisker 153 is soldered or welded to electrode 164 which is suitably a copper electrode. Surrounding and enclosing disc 151 and point contact electrode 153 is glass capsule 155. Glass-to-metal seals 156 and 157 seal capsule 155 to electrodes 164 and 152, respectively. Such an arrangement as this allows the maintenance of any type of desired atmosphere around disc 151, including high vacuum, if desired. It is very easy to make an opening in the glass capsule to provide the desired atmosphere inside and seal off the opening in the glass to maintain this desired atmosphere. Device 158 is then connected by electrical leads 159 and 160 to an alternating current source 161 to be rectified, and an electrical load 162. Suitably, the direct current voltage resulting from the rectified current flowing in the system will appear across resistor 162. Line 163 connects alternating current source 161 and resistor or load 162 completing the electrical circuit. Suitably, alternating current source 161 can be a 110 volt,

60 cycle source or other alternating current source of higher or lower voltage.

Example 8 A type of junction transistor 300 consisting of n-type and p-type materials is shown in FIGURE 13. The transistor assembly shown is of the n-p-n-type, but p-n-p-type is also included in the invention. The section 301 between the two end blocks 3'02 and 303 is called the body, and this forms a common connection between input and output circuits. The emitter is designated by the letter B, the body by B, and the collector by C. Generally, the transistor 300 has its emitter connected to an input terminal 305, and the body connected through a source of power such as a battery 307 to another input terminal 306. The collector 303 of the transistor is connected to an output terminal 304 while the body is connected through a second source of power such as battery 308 to the other output terminal 309. Normally, batteries 307 and 308 will be arranged so that the emitter has a negative polarity with respect to the body, and the collector is positive with respect thereto. However, under certain conditions, it is desirable to reverse the polarities of the batteries 307 and 308. Such a boron-germanium transistor is useful for amplification purposes or any use where conventional vacuum tubes such as triodes or similar devices are required. Typical compositions found useful for a transistor device shown in FIGURE 13 are:

(1) For n-type material, 0.0001 atom percent beryllium in boron-germanium of 0.06 weight percent germanium,

(2) For p-type material, 0.00001 atom percent carbon in boron-germanium of 0.05 weight percent germanium.

A more complete range of compositions useful for transistor applications is shown in Table I. Borongermanium based materials as either por n-type semiconductor materials are optionally used in conjunction with known por n-type semiconductor materials such as silicon, germanium, silicon carbide, etc. In general, transistors are desirably made with relatively low proportions of dopants, such as from 0.0001 weight percent to 0.10 weight percent. However, higher concentrations ranging upward from 1X 10* weight percent to the limits shown in Table I are applicable.

Example 9 A specific example of the thermoelectric cooling of the present invention is a phosphorus furnace for the production of phosphoric anhydride, such as is shown in simplified form in FIGURE 14. Here, 400 is a furnace body into which there is directed a stream of white liquid phosphorus 401 and air 402 or other oxygen source. The oxidation of the phosphorus evolves a tremendous amount of heat which must be dissipated.

Prior art methods for removing heat from phosphorus burners have been based upon cooling water sprays, but because of the furnace wall temperatures in excess of 800 C., such methods are costly.

It has now been found that a phosphorus burner having an exit gas stream 403 containing phosphoric anhydride is readily cooled by contacting the said hot gas stream against a surface containing a body of modified boron-germanium as described above, a preferred material being boron-germanium of broadly 0.05 weight percent to 45 weight percent germanium, preferably 0.5 weight percent to 40 weight percent germanium, and most preferably 1.0 weight percent to 35 weight percent germanium. A specific material has 10 weight percent germanium. The body of each boron-germanium unit A, B, C, and D is connected by electrical leads to an external electrical circuit, so that the thermoelectric cooling occurring in the burner body 400 gives an output of electricity. Multiple thermoelectric units are electrically joined for self-cooling using the circuit shown in FIG- URE 8, which represents a typical circuit by which a device of the type shown in FIGURE 14 can be used for cooling or power generation as the situation requires. Element 99 of FIGURE 8 represents a battery or power source which, when connected thnough a switch element 90, can be used to cool elements A, B, C and D when resistance loads 89 and motor load 98 are cut out of the circuit by appropriate switches, elements 90, 95, 96, or 97. When power generation is desired, battery 99 may be cut out of the electrical circuit and either one or both the loads, elements 98 and 89 powered by the electricity generated by heat converted to electrical power with elements A, B, C, and D.

Example In another embodiment of the invention, p-type (elements 551) and n-type legs (elements 553) are assembled as shown in a cross-sectional view of the device 560 of FIGURE 4. An advantage of this type power generator and cooling device is that a simplified design is possible. Element 567 represents an inner lining of a reactor, exhaust manifold, pipe or other unit which it is desirable to cool or from which heat can be absorbed for the purpose of converting to electricity. Element 568 represents an air or vacuum gap or electrically and thermally insulating material between each pand n-element. Elements 580, 581, 582, 583 and 58 4 represent individual cold junction sections for each p-n combination. Heat is removed from elements 580, 581, 582, 583 and 584 by convection and radiation cooling. When the unit shown in FIGURE 4 is to serve as an energy converter, load 559 is connected through switch 554, with switch 552 open, to the device 560. With a hot gas or heat source inside element 567, heat flows through the wall of element 567, through the individual hot junction leads, elements 590, 591, 592, 593 and 594, then through each p and n leg and thence through the individual cooling sections 580, 581, 582, 583 and 584. When the unit 560 is to be used as a cooling unit, switch 554 is opened and switch 552 is closed connecting unit 560 in series with a power source 558 which causes current to flow in a reverse direction to the case when the unit was producing electric power. The simple p and n legs of the device shown in FIGURE 4 can be replaced with p and n legs of a segmented construction, as typified in Example 4, or with a single boron-germanium based material for each leg. Bonding of the hot and cold junction materials as well as ditfusion barriers between segments of various thermoelectric materials is carried out by the various techniques, e.g., hot-pressing, presented herein.

Thermoelectric devices of the type shown in FIGURE 4 are particularly useful for generating power when such a device is installed as a part of the exhaust system of autos, planes, boats, rockets and other systems where waste heat at temperatures in excess of 400 C. is available.

The present patent application is a continuation-in-part of application Serial No. 824,240, filed July 1, 1959.

What is claimed is:

1. A thermoelectric power generating device which generates power at temperatures of from 110 C. to 925 C. comprising a first element comprising boron in combination with from 0.05 to 45 weight percent of germanium, and a second element in electrical and thermal contact therewith, the second element being comprised of at least one member of the class consisting of carbon, copper, gold, silver, nickel, cobalt, iron, rhenium, vanadium, hafnium, niobium, titanium, tantalum, beryllium and the oxides, borides, carbides, silicides and nitrides of nickel, cobalt, iron, rhenium, vanadium, hafnium, niobium, titanium, tantalum and beryllium, and external leads connected to the respective elements.

2. A thermoelectric power generating device which generates power at temperatures of from 110 C. to 925 C. comprising a first element comprising boron in combination with from 0.05 to 45 weight percent of germanium, and a second element in electrical and thermal contact therewith, the second element being comprised of at least one member of the class consisting of carbon, copper, gold,

silver, nickel, cobalt, iron, rhenium, vanadium, hafnium, niobium, titanium, tantalum, beryllium and the oxides, borides, carbides, and nitrides of nickel, cobalt, iron, rhenium, vanadium, hafnium, niobium, titanium, tantalum, and beryllium, the said second element being characterized by an electrical conductivity and a thermal conductivity which are at least equal in magnitude to the respective electrical and thermal conductivities of the aforesaid first element, and means of electrically connecting the respective elements to an external circuit.

3. A device as described in claim 1, in which the said first element also contains dispersed therein at least one additional chemical element in the proportions:

1X 10* to 18 Weight percent for Li; 1x 10- to 20 weight percent for Ag, Au, Cu, Pb, P, Sb,

As, Bi, S, Se, Te and Po;

1X10" to 25 weight percent for Sr, Ca, Zn, Al, Ga, In, RE, Y, Sc, Nb, Ta, V, Cr, Mo, W, Mn, Re, C0, Fe, Ni, Ru, Ir, and Pd;

1X10 to 0.04 wt. percent for C, Si, Ti, Zr, Be, Sn,

and Hf.

4. A thermoelectric generating material to supply power, the said material consisting of boron containing dispersed therein from 0.05 to 45% by weight of germanium together with a modifying component selected from the group consisting of carbon, aluminum, beryllium, magnesium, silicon, tin, phosphorus, titanium, zirconium, hafnium, cobalt, manganese and the rare earths of type 43;

5. Process for the production of power which comprises applying heat at temperatures from C. to 925 C. to one end of a thermoelectric body while cooling the other end thereof, the said body being provided with electrical leads at the hot and cold ends respectively, and the said body being composed of boron having intimately dispersed therein from 0.05 to 45 weight percent germanium.

6. Process for the production of power which comprises applying heat at temperatures from 110 C. to 925 C. to one end of a thermoelectric body while cooling the other end thereof, the said body being provided with electrical leads at the hot and cold ends respectively, and the said body being composed of boron having intimately dispersed therein from 0.05 to 45 weight percent of germanium, and addition chemical elements in the proportions:

1X 10- to 18 weight percent for Li;

1X10- to 20 weight percent for Ag, Au, Cu, Pb, P, Sb,

As, Bi, S, Se, Te and Po;

1X10" to 25 weight percent for Sr, Ca, Zn, Al, Ga, In, RE, Y, Sc, Nb, Ta, V, Cr, Mo, W, Mn, Re, C0, Fe, Ni, Ru, Ir, and Pd;

1 10 to 0.04 wt. percent for C, Si, Ti, Zr, Be, Sn

and Ht.

7. Process for the production of power which comprises applying heat at temperatures from 110 C. to 925 C. to one end of a thermoelectric body while cooling the other end thereof, the said body being provided with electrical leads at the hot and cold ends respectively, and the said body being composed of boron having intimately dis persed therein from 0.5 to 40 weight percent of germanium.

8. A device for generating electric power when in contact with a region of high temperature, said device comprising at least two thermoelectric bodies in electrical series, the first said body being subjected to the highest temperature and comprising boron containing 0.05 to 45 weight percent of germanium dispersed in the said boron, the first body being in contact with a series of at least another thermoelectric body and external leads connected to the respective bodies.

9. Process for cooling at medium which comprises contacting the said medium with one end of a thermoelectric body composed of boron having dispersed therein from 0.05 to 45 weight percent of germanium, together with 15 a minor proportion of at least one additional element in the following proportions:

1X 10* to 18 weight percent for Li;

1 10- to 20 weight percent for Ag, Au, Cu, Pb, P,

Sb, As, Bi, S, Se, Te and P;

1x10" to 25 weight percent for Sr, Ca, Zn, Al, Ga, In, RE, Y, Sc, Nb, Ta, V, Cr, Mo, W, Mn, Re, C0, Fe, Ni, Ru, Ir and Pd;

1 10 to 0.04 wt. percent for C, Si, Ti, Zr, Be, Sn

and Hf,

the said thermoelectric body having electrical leads connected thereto, and passing a polarized electric current through the said body whereupon the end of the body is cooled and the medium in contact therewith is cooled.

10. A device for generating electric power when in contact with a region of high temperature, said device comprising at least three thermoelectric bodies in electrical series, the first said body being subjected to the highest temperature and comprising boron containing 0.05 to 45 weight percent of germanium dispersed in the said boron, the first body being in contact with a second thermoelectric body consisting of a boron-tin containing body, and the second body being in contact with a third thermoelectric body selected from the group consisting of bismuth telluride and lead telluride.

11. Process for cooling a phosphorus burner which comprises contacting elemental phosphorus with oxygen, with the evolution of heat to form a gas stream containing phosphoric anhydride, and contacting the said hot gas stream against a surface containing a body of boron having dispersed therein from 0.05 to 45 weight percent of ger- 16 manium, the said body having electrical leads thereon whereby electricity is generated and conducted away from the said body to cool the said surface.

12. Process for producing a body of boron containing from 0.05 to weight percent of germanium which comprises pressing together powdered boron and germanium in the desired proportions at a temperature of from 400 C. to the melting point and a pressure of from to 50,000 p.s.i.

13. Process for producing a body of boron containing from 0.05 to 45 weight percent of germanium which comprises pressing together powdered boron and germanium in the desired proportions together with at least one additive in the following proportions:

at a temperature of from 400 C. to the melting point of the composite mixture and a pressure of from 50 to 50,000 p.s.i.

References Cited in the file of this patent UNITED STATES PATENTS Weintraub Nov. 25, 1913 Schroter et a1 Oct. 27, 1936 UNITED STATES PATENT OFFICE CERTHHCATE 0F CORRECTHNN Patent Nb. 3,081,361

March 12, 1963 Courtland M, Henderson et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 20,

for material 61" read material 62 2 2 column 10, line 28, for '(S K)" read (S K)--,

Signed and sealed this 7th day of April 1964,

(SEAL) jtttest:

EDWARD J. BRENNER ERNEST w,

SWIDER Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION March 12, 1963 Patent No. 3,081 ,361

Courtland M. Henderson et a1.

appears in the above numbered pat- It is hereby certified that error ent requiring correction and that the said Letters Patent should read as corrected below.

Column 4,

column 10,

line 20, for "material 61" read material 62 line 28 for "(S K) read (5 K) Signed and sealed this 7th day of April 1964.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J BRENNER Commissioner of Patents 

1. A THERMOELECTRIC POWER GENERATING DEVICE WHICH GENERATES POWER AT TEMPERATURES OF FROM 110* C. TO 925* C. COMPRISING A FIRST ELEMENT COMPRISING BORON IN COMBINATION WITH FROM 0.05 TO 45 WEIGHT PERCENT OF GERMANIUM, 